As worldwide petroleum deposits decrease, there is rising concern over shortages and the costs that are associated with the production of hydrocarbon products. As a result, alternatives to products that are currently processed from petroleum are being investigated. In this effort, biofuel such as biodiesel has been identified as a possible alternative to petroleum-based transportation fuels. In general, a biodiesel is a fuel comprised of mono-alkyl esters of long chain fatty acids derived from plant oils or animal fats. In industrial practice, biodiesel is created when plant oils or animal fats are reacted with an alcohol, such as methanol.
For plant-derived biofuel, solar energy is first transformed into chemical energy through photosynthesis. The chemical energy is then refined into a usable fuel. Currently, the process involved in creating biofuel from plant oils is expensive relative to the process of extracting and refining petroleum. It is possible, however, that the cost of processing a plant-derived biofuel could be reduced by maximizing the rate of growth of the plant source and by minimizing the costs of feeds needed to support the plant growth. Because algae is known to be one of the most efficient plants for converting solar energy into cell growth, it is of particular interest as a biofuel source. However, current algae processing methods have failed to result in a cost effective algae-derived biofuel.
In overview, the biochemical process of photosynthesis provides algae with the ability to convert solar energy into chemical energy. During cell growth, this chemical energy is used to drive synthetic reactions, such as the formation of sugars or the fixation of nitrogen into amino acids for protein synthesis. Excess chemical energy is stored in the form of fats and oils as triglycerides. Thus, the creation of oil in algae only requires sunlight, carbon dioxide and the nutrients necessary for formation of triglycerides. Nevertheless, with the volume requirements for a fuel source, the costs associated with the inputs are high.
One possible source of carbon dioxide and other nutrients that support cell growth is found in flue gases from power plants or other combustion sources. Further, when present in flue gases, these nutrients are considered pollutants that must be properly disposed of. Therefore, use of nutrients from flue gases to support cell growth will abate pollution.
In light of the above, it is an object of the present invention to provide a system and method for producing algae-derived biofuel which reduces input costs. For this purpose, a number of systems have been developed, such as those disclosed in co-pending U.S. patent application Ser. No. 11/549,532 for an invention entitled “Photosynthetic Oil Production in a Two-Stage Reactor,” co-pending U.S. patent application Ser. No. 11/549,552 for an invention entitled “High Photoefficiency Microalgae Bioreactors” and co-pending U.S. patent application Ser. No. 11/549,561 for an invention entitled “Photosynthetic Oil Production with High Carbon Dioxide Utilization,” which are filed concurrently herewith and assigned to the same assignee as the present invention, and are hereby incorporated by reference. Another object of the present invention is to provide a system and method for producing algae-derived biofuel that causes pollution abatement. Still another object of the present invention is to provide a system for supplying nutrients to algae cells in the form of pollutants scrubbed from flue gases. Another object of the present invention is to provide a system for recycling the effluent from a medium for growing algae as a scrubber solution. Another object of the present invention is to provide a system for producing algae-derived biofuel that defines a flow path for continuous movement of the algae, its processed derivatives, and the medium fostering its growth. Yet another object of the present invention is to provide a system and method for producing biofuel from pollutant-fed algae that is simple to implement, easy to use, and comparatively cost effective.